Organic Matter Sulfate Research Articles

Sulfur isotopes of organic matter preserved in 3.45-billion-year-old stromatolites reveal microbial metabolism

The 3.45-billion-year-old Strelley Pool Formation of Western Australia preserves stromatolites that are considered among the oldest evidence for life on Earth. In places of exceptional preservation, these stromatolites contain laminae rich in organic carbon, interpreted as the fossil remains of ancient microbial mats. To better understand the biogeochemistry of these rocks, we performed microscale in situ sulfur isotope measurements of the preserved organic sulfur, including both Δ(33)S and . This approach allows us to tie physiological inference from isotope ratios directly to fossil biomass, providing a means to understand sulfur metabolism that is complimentary to, and independent from, inorganic proxies (e.g., pyrite). Δ(33)S values of the kerogen reveal mass-anomalous fractionations expected of the Archean sulfur cycle, whereas values show large fractionations at very small spatial scales, including values below -15‰. We interpret these isotopic patterns as recording the process of sulfurization of organic matter by H(2)S in heterogeneous mat pore-waters influenced by respiratory S metabolism. Positive Δ(33)S anomalies suggest that disproportionation of elemental sulfur would have been a prominent microbial process in these communities.

Structural alterations of humic acid fractions in a steel slag-compost fertilizer during fertilization. Analysis by pyrolysis/methylation-gas chromatography/mass spectrometry

Alterations in the structural features of humic acids (HAs) in a steel slag-compost fertilizer for supplying soluble Fe(II) to barren ground in coastal areas were monitored during a 6-month period of fertilization. HAs, the major organic fractions in the fertilizer, were extracted at different periods of time (2, 4 and 6 months) in the absence and presence of steel slag. To focus on the polymeric structure of the HA-backbone and the organic fractions, which are sorbed onto the HA-polymeric matrix (e.g., lipids), the extracted HA samples were analyzed by pyrolysis-gas chromatography/mass spectrometry under conditions where the sample is methylated with tetramethylammonium hydroxide (TMAH-py-GC/MS). The structural features analyzable by TMAH-py-GC/MS for the HA were dramatically altered in the presence of steel slag during the fertilization period. The major modification involved a decrease in phenolic moieties and a significant increase in the sulfur-containing pyrolysate compounds. These results indicate that the steel slag has a significant effect in altering the structure of HA in the fertilizer. TMAH-py-GC/MS analysis of the HAs indicated that the sulfur in the HAs was present in an organic form and not as elemental sulfur. Significant increases in the levels of biomarker fatty acids (iso- and anteiso-C15:0 and C17:0 carboxylic acids), which are related to the activity of sulfate reducing bacteria, suggests that the significant alterations in the HA structures in the presence of steel slag can be attributed to the sulfurization of organic matter in the fertilizer to form hydrogen polysulfides by the reduction of sulfate ions in seawater and/or steel slag via microbial processes.

Bacterial calcification as a possible trigger for francolite precipitation under sulfidic conditions

Francolite (carbonate-fluor-apatite) is known to form in sediments where intense organic-matter decay occurs, but under oxic-to-suboxic conditions, because the alkalinity rise accompanying bacterial sulfate reduction (anoxic conditions) increases francolite solubility, hence preventing its supersaturation and precipitation. However, lagoonal, organic matter-rich, cryptalgal carbonates of Jurassic age located in the French Jura Mountains contain francolite that formed during early diagenesis, under anoxic-sulfidic and highly alkaline conditions. To explain this paradoxical situation, we propose the following “chain of reactions”: the presence of abundant biomass in the sediment would supply the “raw material” to the reactional system, i.e., the initial P budget, released through organic decay. The development of cryptalgal, bacterial mats at the sediment–water interface would have limited exchanges between the water column and the pore space, hampering pore water renewal and favoring the early onset of sulfate-reducing reactions. The onset of sulfate reduction would increase pore water alkalinity, potentially preventing francolite precipitation. In addition, the presence of sulfide ions would induce organic matter sulfurization, resulting in a relative pH rise. Alkalinity and pH rises would trigger the development of conditions leading to carbonate supersaturation, inducing bacterial-structure calcification. The sudden fall in alkalinity induced by early calcification would allow francolite precipitation, despite sulfidic conditions.

Molecular characterization of dissolved organic matter in pore water of continental shelf sediments

Dissolved organic matter (DOM) in sediment pore water is a complex molecular mixture reflecting various sources and biogeochemical processes. In order to constrain those sources and processes, molecular variations of pore water DOM in surface sediments from the NW Iberian shelf were analyzed by ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) and compared to river and marine water column DOM. Weighted average molecular element ratios of oxygen to carbon ((O/C) wa) and hydrogen to carbon ((H/C) wa) provided general information about DOM sources. DOM in local rivers was more oxygenated ((O/C) wa 0.52) and contained less hydrogen ((H/C) wa 1.15) than marine pore water DOM (mean (O/C) wa 0.50, mean (H/C) wa 1.26). The relative abundance of specific compound groups, such as highly oxygenated aromatic compounds or nitrogen-bearing compounds with low H/C ratios, correspond to a high concentration of lignin phenols (160 μg/g sediment dry weight) and a high TOC/TN ratio (13.3) in the sedimentary organic matter and were therefore assigned to terrestrial sources. The lower degree of unsaturation and a higher relative abundance of nitrogen-bearing compounds in the pore water DOM reflected microbial activity within the sediment. One sampling site on the shelf with a high sediment accumulation, and a humic-rich river sample showed a wide range of sulfur compounds in the DOM, accompanied by a higher abundance of lipid biomarkers for sulfate-reducing bacteria, probably indicating early diagenetic sulfurization of organic matter.

Investigating pathways of diagenetic organic matter sulfurization using compound-specific sulfur isotope analysis

We present the results of compound-specific sulfur isotope analyses performed on organic sulfur compounds (OSCs) isolated from sediments deposited in the euxinic Cariaco Basin, Venezuela. Individual OSCs (sulfurized highly branched isoprenoids and malabaricatriene) have sulfur isotope compositions of ca. −15‰, which is 34S enriched by 5–15‰ relative to coeval bulk organic and inorganic sulfur pools. These observed differences in the sulfur isotope composition of bulk organic sulfur in the kerogen and bitumen pools and individual OSCs demonstrate that there are multiple pathways of organic sulfur formation operating simultaneously in marine sediments. Comparison of our measured compound-specific sulfur isotope data with values predicted using simple isotopic mass balance assumptions suggests that the sulfurization process likely involves multiple sources of inorganic sulfur. Further, the isotopic composition of these various precursor inorganic sulfur species and the specific pathway of sulfur incorporation into organic matter (OM) impart distinct isotopic compositions to the resulting organic sulfur compounds. These data represent the first compound-specific sulfur isotope measurements made in marine sediments, and demonstrate the utility of compound-specific sulfur isotope analysis in identification of inorganic sulfur sources for OM sulfurization and tracking pathways of sulfur incorporation, which will lead to a more complete understanding of diagenetic sulfurization of OM.

Redox sensitivity of P cycling during marine black shale formation: Dynamics of sulfidic and anoxic, non-sulfidic bottom waters

A high-resolution geochemical record of a 120 cm black shale interval deposited during the Coniacian–Santonian Oceanic Anoxic Event 3 (ODP Leg 207, Site 1261, Demerara Rise) has been constructed to provide detailed insight into rapid changes in deep ocean and sediment paleo-redox conditions. High contents of organic matter, sulfur and redox-sensitive trace metals (Cd, Mo, V, Zn), as well as continuous lamination, point to deposition under consistently oxygen-free and largely sulfidic bottom water conditions. However, rapid and cyclic changes in deep ocean redox are documented by short-term (∼15–20 ka) intervals with decreased total organic carbon (TOC), S and redox-sensitive trace metal contents, and in particular pronounced phosphorus peaks (up to 2.5 wt% P) associated with elevated Fe oxide contents. Sequential iron and phosphate extractions confirm that P is dominantly bound to iron oxides and incorporated into authigenic apatite. Preservation of this Fe–P coupling in an otherwise sulfidic depositional environment (as indicated by Fe speciation and high amounts of sulfurized organic matter) may be unexpected, and provides evidence for temporarily non-sulfidic bottom waters. However, there is no evidence for deposition under oxic conditions. Instead, sulfidic conditions were punctuated by periods of anoxic, non-sulfidic bottom waters. During these periods, phosphate was effectively scavenged during precipitation of iron (oxyhydr)oxides in the upper water column, and was subsequently deposited and largely preserved at the sea floor. After ∼15–25 ka, sulfidic bottom water conditions were re-established, leading to the initial precipitation of CdS, ZnS and pyrite. Subsequently, increasing concentrations of H 2S in the water column led to extensive formation of sulfurized organic matter, which effectively scavenged particle-reactive Mo complexes (thiomolybdates). At Site 1261, sulfidic bottom waters lasted for ∼90–100 ka, followed by another period of anoxic, non-sulfidic conditions lasting for ∼15–20 ka. The observed cyclicity at the lower end of the redox scale may have been triggered by repeated incursions of more oxygenated surface- to mid-waters from the South Atlantic resulting in a lowering of the oxic–anoxic chemocline in the water column. Alternatively, sea water sulfate might have been stripped by long-lasting high rates of sulfate reduction, removing the ultimate source for HS − production.

Spatial and seasonal variations in depth profile of trace metals in saltmarsh sediments from Sapelo Island, Georgia, USA

This study was undertaken to elucidate the impact of early diagenetic processes on the accumulation of trace metals in Sapelo Island saltmarsh sediments as a function of time, space and sediment properties. Samples were collected from three sites in summer (May 1997) and winter (January 1998) along a transect from an unvegetated Creek Bank through a vegetated Tidal Levee to the vegetated midmarsh with evident lateral heterogeneity caused by hydrologic regime, macrophytes and microbial and macrofaunal activities. A suite of trace metals (As, Ba, Cr, Co, Cu, Cd, Mo, Ni, Pb, Th, Ti, U, V, Zn and Zr) was analyzed to obtain their depth-distribution at the three sites. Spatially marked differences were observed, that were primarily related to hydraulic flushing of trace metals away from the sites in high-energy regimes, rapid downward mixing and reworking of sediment via bioturbation, and below-ground degradation and production of Spartina biomass. Although sulfate reduction and the formation of acid volatile sulfide and pyrite were dominant processes throughout the marsh, the trace metal scavenging role of sulfides was not apparent. However, possible sulfurization of organic matter, leading to enhanced trapping of trace metals with organic carbon, may have played an important role in sequestration of trace metals. No similarity was observed visually between the depth trends of trace metals and sediment properties (grain size, iron-oxyhydroxide content, acid volatile sulfides and pyrite content) that are known to play a major role in trace metal partitioning. Only organic carbon content closely followed the trace metal profiles at all the three sites. Minor variation in depth-integrated sediment trace metal content was observed seasonally at each of the three sites. Furthermore, the depth trend of profiles of individual trace metals also did not vary significantly over the seasons either.

Enhanced trapping of molybdenum by sulfurized marine organic matter of marine origin in Mesozoic limestones and shales

There have been many studies devoted to trace metals and their value in assessing the paleoredox conditions of ancient marine deposition. Among them, molybdenum (Mo) is frequently cited as an effective proxy for sediments and sedimentary rocks. Recently, Helz et al. (Helz, G.R., Miller, C.V., Charnock, J.M., Mosselmans, J.L.W., Pattrick, R.A.D., Garner, C.D., Vaughan, D.J., 1996. Mechanisms of molybdenum removal from the sea and its concentration in black shales: EXAFS evidences. Geochim. Cosmochim. Acta, 60, 3631–3642) and Adelson et al. (Adelson, J. M., Helz, G. R., Miller, C. V., 2001. Reconstructing the rise of recent coastal anoxia; molybdenum in Chesapeake Bay sediments. Geochim. Cosmochim. Acta, 65, 237–252.) suggested that Mo does not behave conservatively in the water column when H 2S reaches a threshold concentration. Above this concentration, a “switch” operates, and Mo is scavenged by forming bonds with metal-rich (notably iron) particles, sulfur-rich organic molecules and pyrite. In this paper, Mo-trapping by sulfur-rich organic matter (OM) in ancient marine deposits is emphasized. The following Mesozoic geological formations were selected for study because of their relatively high concentration of sulfurized OM: the Akkuyu Formation (Turkey), the Calcaires d'Orbagnoux (France) and Kimmeridge Clay (UK) and its timeequivalent in Boulonnais (France), the Kashpir oil shales (Russia), and the La Luna Formation (Venezuela). The sulfur-rich OM is identified by either measured organic-S abundance or kerogen microscope observation. Our results show that Mo is systematically more enriched relative to the other redox-sensitive/sulfide-forming elements studied (U, V, Ni, Cu, Zn, Cr), and Mo enrichment is positively correlated with the amount of sulfurized OM but not with pyrite abundance. These results illuminate the role played by sulfurized OM in geologic-scale Mo capture and retention, but they also underline the role played by reactive iron. Significant OM sulfurization is only possible when reactive iron is limited. Nevertheless, pyrite formation, though limited, could act as an initial Mo trap, prior to Mo uptake by OM that is sulfurized after the pyritization step. In future paleoenvironmental reconstructions, attention must be paid to this enhanced Mo enrichment in the presence of sulfurized organic matter. In such cases, the use of Mo could lead to overestimation of the reducing conditions of the depositional environment.

Mechanisms of sulfur introduction chemically controlled: δ34S imprint

Organic sulfur in marine sediment is 34S enriched relative to the co-existing pyrite. This phenomenon is still enigmatic. Timing of the sulfur incorporation, immobilization and different sulfur species involved are part of the explanations. The reduced sulfur species incorporation into organic matter (OM) is generally assumed to have negligible δ 34S fractionation. This assumption has never been confirmed by laboratory experimental data. The present study measures the δ 34S changes resulting from reduced sulfur species (sulfides and polysulfide anions) incorporation into organic model compounds in an aquatic and low temperature (25 °C) system that simulates diagenetic marine environment. In addition, we also investigate the δ 34S fractionation and the isotope chemical mixing in the formation of polysulfide anions produced from elemental sulfur and sulfide anions. The results showed total isotope mixing between the two species in the formation of polysulfides. Acidification of the polysulfides solution caused δ 34S fractionation between the released elemental sulfur and H 2S. The incorporation of polysulfides and sulfides into carbonyl groups, caused 34S enrichment relative to the starting polysulfides and sulfide of 4–5‰. The 34S enrichment of the sulfurized carbonyl groups showed a minimal effect by temperature (0–70 °C) and is not affected by salinity, polysulfides composition, reaction time or solubility in water. The incorporation of polysulfides and sulfides into brominated organic compounds was negligibly 34S enriched. The chemical mechanisms controlling the polysulfides incorporation into OM depend mostly on the functional groups and determine the 34S enrichment of the sulfurized OM. The results presented in this study can explain part of the difference between pyrite δ 34S and sulfurized OM δ 34S in natural marine sediments.

Influences of Low‐Temperature Hydrothermal Fluids on the Re‐distributions and Occurrences of Associated Elements in Coal — A Case Study from the Late Permian Coals in the Zhijin Coalfield, Guizhou Province, Southern China

Abstract The occurrences of associated elements and their genetic factors in the No. 30 coal seam in the Zhijin Coalfield were studied using instrumental neutron activation analysis, inductively coupled plasma‐atomic emission spectroscopy, and a scanning electron microscope equipped with an energy‐dispersive X‐ray analyzer. And, a microscope photometer system (Leitz MPV‐III) was used to observe the characteristics of coal petrology. According to the influence degree by the siliceous low‐temperature hydrothermal fluids, the organic matter is divided into four types: A, B, C, and D of the hydrothermally‐altered organic matter (HAOM). The study shows that the high content of Fe (2.31%) is not from pyrite, but mostly from the siliceous low‐temperature hydrothermal fluids. The occurrences of the associated elements in the four organic matter types are different. The contents of Fe, Si, and Al are decreasing, but S and Cu are increasing in the order of the HAOM‐A, HAOM‐B, HAOM‐C, and HAOM‐D. The losing rate of sulfur in organic matter is 0.35% and the content of Fe taken from the low‐temperature hydrothermal fluids into the organic matter is 0.794% during the siliceous low‐temperature hydrothermal fluids invading the coal seam. The above facts indicate that the low‐temperature hydrothermal fluids play a crucial role in the re‐distributions and occurrences of associated elements in coal.

Biogeochemical Characteristics of Lacustrine Sediments Reflecting a Changing Alpine Neotropical Ecosystem during the Pleistocene

Continuous lacustrine deposits of the Funza-II core from the Bogotá basin, Colombia (5°N74°W) record late Pleistocene climatic variations, providing an opportunity to assess the influence of glacial–interglacial climate changes on alpine ecosystems in equatorial South America. Biogeochemical response of this tropical alpine system to climate change was inferred from changes in elemental concentrations and ratios and isotopic signatures in the upper 120 m of the lacustrine Funza core. Values of δ 13C org exhibit eight abrupt, positive shifts that are thought to reflect rapid expansions of C 4 grasses in the tropical Andes and algal blooms. One of these excursions, interpreted to correspond to C 4 vegetation expansion, occurred in sediments accumulated during the last glaciation (∼30,000–50,000 yr B.P.) and implies a downslope shift of the upper Andean treeline, regardless of prevailing temperatures. Sedimentary carbon/sulfur ratios are low and indicate significant sequestering of sulfur. Monosulfides are the dominant constituent of sedimentary sulfur during relatively humid intervals, when increased supply of iron caused by enhanced weathering favored the formation of monosulfide minerals under strongly reducing conditions. In contrast, organosulfur compounds dominate the sedimentary sulfur-species in relatively drier intervals when mildly reducing conditions and limited iron input promoted the diagenetic incorporation of sulfur in organic matter. Dry events inferred from the sulfur record typically correlate with glacial maxima, whereas glacial terminations are usually associated with wet periods.

Biogeochemical controls on reaction of sedimentary organic matter and aqueous sulfides in holocene sediments of Mud Lake, Florida

The distribution and quantity of organic sulfur and iron sulfur species were determined in the Holocene sediments from Mud Lake, Florida. The sediments of this shallow, sinkhole lake are characterized by high sulfur and organic carbon contents as well as active sulfate reduction. They record a shift from a basal peat (below 2 m) comprised of water lily-dominated organic matter to the present cyanobacterial/algal-dominated lake deposit (upper 1 m). This shift in depositional environment and subsequent organic matter source was accompanied by variation in the amount of reactive iron delivered to the sediments, which in turn influenced the type and extent of organic matter sulfurization. Extractable intramolecular organic sulfur is principally found as C 25 highly branched isoprenoid (HBI) thiolanes. Extractable polysulfide-linked lipids, determined by selective chemical cleavage with MeLi/MeI and analyzed as methylthioethers (MTE), are dominated by n-alkanes with sulfur attachments at position 1 and 2, as well as lower amounts of C 25 HBI-MTE. The δ 13C values and carbon-chain length distribution of both series of n-alkylMTE indicate that they are derived from distinct biological precursors. Among the n-alkylMTE with sulfur attachment at position 1 there are three homologous series: one saturated and two with both cis and trans enethiol isomers. The identification of the enethiol in the sulfur-linked macromolecules indicates that n-alkylaldehydes are precursors lipids. The intervals of high concentration of bulk organic sulfur and sulfurized lipids coincide with the intervals of high mineral sulfur content (acid volatile sulfide and chromium reducible sulfur). We suggest that the main control on the enhanced addition of sulfur to the organic matter in Mud Lake was the increased formation of polysulfides during the reduction of iron hydroxides and the subsequent reaction of those polysulfides with mildly oxidized sedimentary organic matter.

Clues to early diagenetic sulfurization processes from mild chemical cleavage of labile sulfur-rich geomacromolecules

Macromolecular fractions, isolated from the solvent extract of sulfur-rich Recent (Siders Pond, USA; Lake Cadagno, Switzerland; Walvis Bay, Namibia) and immature sediments (Gibellina, Messinian of Sicily; Vena del Gesso, Messinian of Italy), were investigated by chemical degradation using sodium ethanethiolate/methyliodide. This mild reagent which cleaves polysulfide bonds to yield methylsulfides has the advantage over other methods of leaving intact other functionalities (like double bonds) and preserving sulfur atoms at their incorporation site. The method is, therefore, well-suited to the molecular level investigation of sulfur-rich macromolecules from Recent sediments containing highly functionalized polysulfide-bound subunits. In Recent anoxic sulfur-rich sediments, the release of various methylthioethers clearly demonstrates that intermolecular sulfurization of organic matter does occur at the earliest stages of diagenesis. Steroids and phytane derivatives are the major sulfurized lipids, a feature also observed in more mature sulfur-rich sediments. Several phytene derivatives, such as cis and trans 1-methylthiophyt-2-enes, as well as methylthiosteroids, including 5α- and 5β-3-(methylthio)-cholest-2-enes, were identified by comparison with synthesized standards. Steroid methylthioenolethers are released from polysulfide-bound steroid enethiols present in the macromolecular fractions. The latter, which correspond to thioketones, can be considered as intermediates in the reductive sulfurization pathway leading from steroid ketones to polysulfide-bound saturated steroid skeletons and are characterized for the first time in the present study. Thus, it could be shown that the major part of the polysulfide-bound lipids occurring in Recent sediments is apparently the result of sulfurization processes affecting carbonyls (aldehydes and ketones). The unsaturated methylthioethers obtained from Recent sediments were not present in more mature evaporitic samples, which suggests that polysulfide-bound unsaturated thiols are intermediates formed during the first sulfurization steps occurring soon after deposition and that they are rapidly transformed by various processes taking place during early diagenesis, notably to yield their saturated counterparts.

Timing of early diagenetic sulfurization of organic matter: a precursor-product relationship in Holocene sediments of the anoxic Cariaco Basin, Venezuela

The incorporation of reduced inorganic sulfur into organic matter is a significant mechanism for the preservation of functionalized organic compounds in the sedimentary environment, but the timing of this process is not currently known. Analysis of organic matter in the Holocene and latest Pleistocene sediments of the Cariaco Basin indicates conversion of a triunsaturated tricyclic triterpenoid, (17E)-13β(H)-malabarica-14(27),17,21-triene, identified by isolation and subsequent one- and two-dimensional 1H and 13C NMR spectroscopy, to a monounsaturated triterpenoid thiane through incorporation of reduced inorganic sulfur species into the isoprenoid side chain within the upper 6 m of sediments. Time control provided by AMS 14C dates was used in conjunction with measured relative abundances of the two compounds to calculate the reaction rate for the sulfurization of this triterpenoid, and empirically determine the first order rate constant (2 × 10 −4 yr −1) for the reaction. This is the first time that such a precursor-product relationship has been positively identified for a sulfurization reaction in sediments.

Anaerobic degradation of organic matter controlled by productivity variation in a restricted Late Triassic basin

The organic-rich late Triassic Kössen Formation (Hungary) was deposited in a shallow basin, situated between a carbonate platform and the continent. A large number (107) of samples of a 240 m thick, steeply dipping core section of the Kössen Fm., built up of mostly non-bioturbated sediments have been analysed by Rock-Eval pyrolysis. Organic petrographic studies, sulphur and iron speciation (total sulphur, HCl-soluble sulphate sulphur, pyrite iron and HCl-soluble iron) and CO 2 measurements have been carried out on smaller sample sets. According to Rock-Eval pyrolysis and organic petrography the immature organic matter (OM) is of dominantly marine origin throughout the section. Unicellular planktonic algae are remains of the most important organic constituents but microbial-algal mat material is also of importance. The carbonate and TOC contents and HI values display much scatter and upward decreasing trends. Type II-S OM is common in the lower third of the section and it occurs in its middle interval, too. The marked downward decrease of T max values is explained by the downward increase of the OM sulphur content. The original organic carbon content (TOC or) was calculated. The degree of OM preservation, expressed in term of TOC/TOC or, varies between 0.36 to 0.89 and shows an upward decreasing trend, interrupted by high values around the middle of the section. This strengthening of the degradation during the black shale event was the result of the parallel decreasing rate of sedimentation and OM deposition. The high TOC/TOC or values found around the middle of the section are mostly the result of a temporary acceleration of OM deposition. Sulphur richness of the OM shows no positive correlation with the degree of organic preservation. Sulphur partitioning between pyrite and OM was controlled by the ratio of reactive iron to OM. Average rates of planktonic productivity ( C prod) vary between 6–9 and 60–88 t C org/m 2/Ma. The rough covariance of the degree of preservation and C prod suggests that variations in planktonic productivity exerted a strong control on preservation in the suboxic, low to medium productivity Kössen Formation.

Sulphur Isotope Partitioning during Formation of Pyrite and Incorporation of Sulphur into Organic Matter in Eastern Mediterranean Sapropels

The Neogene sedimentary record of the eastern Mediterranean is characterized by the occurrence of organic-rich layers. The formation of these 'sapropels' is thought to have been initiated by palaeoclimatic-related increased productivity in the surface waters and/or enhanced preservation of organic matter (OM) due to oxygen-depletion in stagnant bottomwaters. The sapropels contain high contents of inorganic reduced sulphur species (mainly pyrite) derived from the microbial dissimilatory sulphate reduction (Passier et al., 1998). Under conditions of high abundant dissolved reduced or intermediate sulphur species, OM can be sulphidized leading to a reduction of the lability and thus an enhancement of the overall preservation of OM (e.g. Sinninghe Damst6 and de Leeuw, 1990). Here, we present the contents and sulphur isotopic signatures of pyrite and sulphur in OM. A model for organic sulphur formation and the timing with respect to pyrite formation is proposed.

Photochemical Sulfurization of Sedimentary Organic Matter: A Widespread Process Occurring at Early Diagenesis in Natural Environments?

The possibility of light induced formation of sedimentary organo-sulfur compounds has been investigated with simulation experiments. These experiments, using mono- and diunsaturated hydrocarbons and reduced sulfur species, in particular H 2S and elemental sulfur, were conducted under mild conditions (sunlight, low temperature) likely to occur in the photic zone of anoxic environments. These experiments showed an efficient sulphurization of the organic matter under sunlight conditions leading to the formation of organo-sulfur compounds, such as thiophenes and sulfur cross-linked macromolecules, very similar to those occurring in sediments deposited in anoxic environments. These results show the potential for photochemically induced sulfurization of organic matter in environments with photic zone anoxia. Such a process would be especially favored in evaporitic environments with a shallow anoxic boundary extending well into the photic zone.

Thioketones as key intermediates in the reduction of ketones to thiols by HS − in natural environments

Thioketones have been shown to be likely intermediates in the reduction of ketones and aldehydes to thiols by hydrogen sulfide ions, a reaction which plays an important role in the natural sulfurization of organic matter in sediments. The reduction proceeds by a thiophilic addition of HS − on the thioketone most likely via a single electron transfer mechanism.

EFFECTS OF INTENSIVE VEGETABLE PRODUCTION ON CHEMICAL PROPERTIES AND NUTRIENT MINERALIZATION OF A BRITISH COLUMBIA HUMISOL

A study was conducted to determine the effects of long-term vegetable production on some organic matter (OM) chemical properties in an organic soil located near Cloverdale, British Columbia. Producers in this area are concerned about yield reduction and some feel this is due to changes in the soil quality. Paired soil samples were collected from two transects: one in a 40-yr-old vegetable field, and the other in an adjacent fence row. The transects were positioned in order to collect samples from a relatively deep organic deposit and from a shallow deposit where a ridge of mineral subsoil had been exposed. Initial analysis showed that cultivation had changed some chemical properties only in the plow layer. The exception was pH which was higher throughout the sample depth of the cultivated transect. Organic matter loss from the cultivated field was estimated 28% by weight, based on ash accumulation. In the cultivated deep organic section (west of the ridge) OM and C contents were reduced by 7.1 and 5.6% respectively, whereas on the cultivated ridge OM, C, N and S contents and the amount of C, N and S mineralized were reduced by 43.3, 41.6, 43.4, 25.9, 42.8, 60.8 and 52.5%, respectively. On an ash-free basis there were no changes in the deep organic section. In the ridge, the OM sulphur content had increased and the amount of N and S mineralized were decreased compared with the uncultivated transect. In the cultivated surface layer, increased S content in the OM was caused by incorporation of a S-rich subsurface layer during tillage operations. Increases in P content in the cultivated transect were attributed to P fertilization. Within the cultivated transect, C, N and S contents in the exposed mineral ridge were 48, 48, and 44%, respectively, lower than in the deep organic surface layer on the west side of the ridge. The C:N ratios were unchanged at about 16. The chemical stability of the OM was attributed to its well-decomposed nature. At this particular site, the degradation due to excessive cultivation was manifested mainly in OM loss, rather than in changes in OM quality. The main concern of producers is to reduce or prevent further loss of soil OM. Key words: Humisol, organic soil, cultivation, mineralizable C, N and S, incubation

Stable isotope geochemistry of sphalerite and other mineral matter in coal beds of the Illinois and Forest City basins

Cleat and clastic dikes of Middle Pennsylvanian-age coal beds of the Illinois and Forest City basins of Illinois, Iowa, Missouri, and Kansas locally contain appreciable amounts of sphalerite within a kaolinite-pyrite-sphalerite (+ or - pyrite)-calcite paragenetic sequence. The sphalerite and associated minerals are of interest as a partial record of the history of fluids in the sedimentary basin and as possible indicators of Mississippi Valley-type mineralization. Moreover, zinc from the sphalerite may represent an exploitable by-product of coal mining and combustion.Pyrite is abundant in these coals both as fine-grained disseminated framboids that formed during early diagenesis and as coarser grained cleat fillings, etc., that formed much later. The delta 34 S values of this later pyrite, the sphalerite, and the coal organic matter range from -12 to 19 per mil. Within individual samples, however, pyrite, sphalerite, and organic matter sulfur delta 34 S values are nearly identical. This similarity strongly suggests related origins. The delta 34 S values of pyrite, sphalerite, and organic matter from coals of the Illinois basin and the central and southern Forest City basin range from -12 to 0 per mil. This range is not unique to the sphalerite-bearing coals; pyrite and organic matter from sphalerite-free high sulfur coals have similar delta 34 S values (Price and Shieh, 1979). We believe that sulfur produced by the breakdown of organosulfur compounds in the coal is incorporated into the epigenetic sulfides. In the northern Forest City basin, however, many samples have delta 34 S values between 8 and 19 per mil. These are similar to the delta 34 S values of sphalerite and pyrite from the Upper Mississippi Valley Zn-Pb district which lies northeast of the Forest City basin and north of the Illinois basin. This similarity suggests input from a Mississippi Valley-type hydrothermal system.Cleat kaolinite has delta D values of -36 to -24 per mil and delta 18 O values of 19.2 to 20.2 per mil. Assuming that clearing postdated the lignite rank of coalification implies that kaolinite was deposited between 40 degrees and 100 degrees C. At the lower temperatures, the kaolinite fluid would have had an isotopic composition similar to seawater; at the higher temperatures, it would have had a composition similar to the sphalerite-depositing fluid. Sphalerite was deposited from a fluid that was chemically and isotopically similar to the fluids responsible for the main-stage ores of the Upper Mississippi Valley Zn-Pb district (75 degrees -113 degrees C, approximately 21 equiv wt % NaCl, delta D = -65 to -3ppm, and delta 18 O = -0.9-9.9ppm). The isotopic compositions (delta 13 C = -12.4 to -2.7ppm and delta 18 O = 21.1-25.8ppm) and paragenetic positions of the cleat calcite samples are similar to those of the late-stage calcite of the Upper Mississippi Valley Zn-Pb and Illinois-Kentucky fluorspar districts. Calcite inclusion fluids had delta D (sub H 2 O) values of -80 and -58 per mil, implying a meteoric water source. At probable temperatures of 15 degrees to 75 degrees C, this calcite formed from fluids having calculated delta 18 O (sub H 2 O) values of -9 to 1 per mil, implying slight to moderate exchange with sedimentary rocks. The diagenetic-epigenetic history of fluids recorded by the cleat minerals probably began with a slightly evolved seawater, followed by a metal-bearing deep basin brine, and concluded with a cooler, slightly evolved, meteoric-water fluid.